<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>堆快照监控内存</title>
</head>
<body>
  <button id='btn'>add</button>
  <script>
    // 新建 DOM 不放在界面，只是引用它
    var tmpEle

    function fn() {
      var ul = document.createElement('ul')
      for(var i = 0; i < 10; i++) {
        var li = document.createElement('li')
        ul.appendChild(li)
      }

      tmpEle = ul

      // 可将 tmpEle 置为空，清除 DOM 节点
      tmpEle = null
    }

    document.getElementById('btn').addEventListener('click', fn)
  </script>
</body>
</html>